The present invention relates to automatic wire dispensing machines and more particularly to an automatic wire dispensing machine that is capable of dispensing wire from heavy spools under demanding conditions of use that include high rates of wire feed and intermittent and sporadic feed requirements. Such demanding uses are typical in wire spring forming machines and to a certain extent in automatic welding machines that use welding wire as a source of the metal forming the weld bead.
Many industrial operations require a substantially continuous supply of metal wire. An automatic spring making machine is one type of operation, and an automatic welding machine employing wire to form the weld bead is another type of operation. For exemplary purposes, the present invention will be described in connection with these types of operations, although it can be used in other types of operations as well.
In operations requiring a continuous supply of metal wire, the wire can be provided in a number of forms. It can be wound on a wooden spool or it can be packaged in a drum or loosely in a coil. The wire can be mounted for rotation and dispensation about a vertical or horizontal axis.
In order to maximize the efficiency of wire feeding operations, it is desirable to employ supply wire in large quantities; for example, a wire spool weighing up to one thousand (1,000) pounds or more is common. A large supply of wire minimizes the number of times that the spool has to be changed and handled and can provide efficiencies in purchasing the wire in larger bulk quantities.
Large spools of wire present special problems. Because of the inertia of a full spool, a substantial amount of force is required to start the spool rotating, and when wire usages stops, the inertia of the spool causes the spool to continue rotating and continue feeding wire. When relatively thin wire is coiled on a large spool, the problems are especially acute. A sudden start of the spool can break the wire. Moreover, excess tension in the wire can stretch it to the point of "necking down" to a reduced diameter and correspondingly reduce the diameter of the metal available for the metal forming operation. When a particular diameter of wire is accurately predetermined, it is undesirable to stretch the wire so that an inconsistently thinner wire is actually available for the operation.
Another problem with requiring a large pulling force to remove wire from a supply spool is that the wire can be wedged between adjacent coils on the spool and can become gripped tightly enough to resist pulling free of the spool. Further, the drive mechanism for the metal forming operation needs to grip the wire tightly in order to overcome the inertia of the spool, and in so doing the teeth of the drive mechanism can bite into the wire and affect the characteristics of the wire.
Still another problem with the use of a large wire supply spool is that the weight of the spool changes markedly as wire is withdrawn from the spool, reducing the weight of a fully loaded spool from one thousand (1,000) pounds to as little as thirty (30) pounds when the spool is empty. This presents a changing inertia force that affects the starting and stopping characteristics of the spool.
A number of machines have been developed to overcome these problems, but none have been completely successful. Most such machines employ some type of motorized mechanism for supplying the wire and a mechanical brake mechanism for stopping the spool when the wire supply is no longer required. Some machines provide tension control devices that are intended to match the feed rate with the utilization rate. Other machines provide slack wire loops that permit the machine using the wire to make rapid and intermittent use of the wire while providing the wire feed at a more continuous rate. Such machines often require frequent adjustment to accommodate different sizes of wires, different feed rates, different spool sizes, and changing spool weights due to the removal of wire from the spools. Even with continuous changes, such machines still are usually not capable of consistent and reliable performance.
It is an object of the present invention to provide an improved automatic motorized wire dereeler or dispenser that is simple to operate, compact, inexpensive, and accommodates a wide range of operating conditions without adjustment.